This invention is directed generally to the theatrical and stage lighting arts, and more particularly to a novel and improved lighting control system which may advantageously be used in connection with the control of stage or theatrical type lighting.
Stage and theatrical lighting systems generally make use of a variety of lamp types which require a corresponding variety of power sources for their operation. Such systems or installations may include a number of different types and kinds of lighting for use at different times and/or for different applications. Such lamps may include, for example, high pressure arc lamps which require relatively high start-up voltages, i.e., which may be from two to five times the lamp's normal operating voltage, depending on the particular lamp characteristics. Such high pressure arc lamps usually require a series ballast to reduce the voltage at the lamp terminals.
Moreover, it is often desirable to provide light dimming circuits for controlling the intensity of lamps in such a stage or theatrical lighting system, either individually or collectively, as desired.
Heretofore, electrical control systems for such lighting installations have been relatively large and cumbersome, requiring many large and relatively expensive electrical components. This has been necessary in order to accommodate the desired range of control of operating voltages, dimming, and the like, for a large number of lamps, which, as indicated above, may have varying electrical operating requirements. Moreover, it has heretofore been necessary to provide a completely separate electrical control system in order to change the operating line voltage, and often even in order to operate at a different line frequency. That is, for example, standard U.S. "house current" is 120 volts 60 hertz, whereas many European systems provide 220 volts 50 hertz current. Such lighting control systems have further heretofore required relatively large, heavy and cumbersome choke coils, transformers, wire-wound rheostats, and the like to provide a desired range of start-up and dimming controls for a large number of lights in a given system or installation.
Moreover, such systems have heretofore generally been incapable of operating different lamps which may be used in such a lighting system or installation. For example, lamps of 12 volts, 28 volts, 60 volts, 90 volts or 120 volts may be selected for use in a given system. Generally speaking, the lower voltage lamps are less expensive and are often preferred by lighting technicians. Moreover, with systems heretofore in use, lamp life is often unduly shortened, because of lack of adequate control over the voltages and current supplied to the lamps during operation. Also, in the case of short circuits or overloading of the system, present control systems often fail to provide adequate protection for the lighting equipment.
Importantly, our new lighting control circuit allows the addition of dimmers for controlling a large number of high wattage lamps either individually or collectively, while avoiding much of the expensive and cumbersome equipment associated with the prior art dimmer and control systems. For example, early versions of theatrical light dimmer systems involved cabinets some eight feet tall, four feet deep and six feet wide, weighing 1,000 pounds or more. These systems were clearly not portable in nature, and moreover usually offered a maximum of only 12 dimmer controls. Moreover, these units operated only with 120 volt AC lamps and offered no flexibility whatever for lamp interchangeability. More recent technology offers more compact packages, on the order of only 12 to 20 inches in length, width and depth. However, such controls generally weigh from 65 to 85 pounds for 12 dimmers. Moreover, these newer system still do not permit lamp interchangeability, but are generally designed to operate in connection with only one lamp type.
Furthermore, the prior art systems generally did not accommodate changes in lamps or operating voltages because relatively heavy and expensive components such as power SCRs and heavy-duty toroidal filters were generally custom manufactured for operation with but a single type of lamp and at a single voltage. Larger dimmer systems generally were proportionately larger, more complex and more expensive than the above-mentioned 12 dimmer type of system. For example, many installations, both permanent and portable, require as many as from 96 to 200 dimmer modules or dimmer controls. Such systems, generally referred to in the art as a "high density rack", are both heavy, complex and expensive, and yet offer surprisingly little flexibility in their operation. By way of example, high density racks systems presently available do not offer switchable lamp voltages or short circuit protection. The approximate weight per dimmer control of these systems runs from three to five pounds. Moreover, such systems require a minimum of a 10 watt load for safe operation and generally offer output power at only 120 volts.